2017 | 70/3 | 201–213 | 12 Figs. | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society Geologia Croatica The relationship of the geological framework to the Quaternary aquifer system in the Sava River valley (Croatia) Željka Brkić Croatian Geological Survey, Department of Hydrogeology and Engineering Geology, Sachsova 2, 10000 Zagreb, Croatia; ([email protected]) doi: 10.4154/gc.2017.12 Abstract Article history: Data from approximately 500 boreholes and an additional 40 wells for which there is a plausible Manuscript received February 02, 2017 range of data, facilitate description of the geometry of the Quaternary aquifer and its character- Revised manuscript accepted May 05, 2017 istics respectively, and pretension of the elements of the conceptual hydrogeological model in Available online October 31, 2017 the Sava River valley. The aquifer heterogeneity is caused by tectonic activity and the deposi- tional environments of the sediments within the valley. In the wider Zagreb area, gravel is the dominant component of the aquifer. Downstream from Zagreb, the aquifer is composed mainly of sand with sporadic intercalations of gravel. An admixture of silt and clay is not uncommon within the sand. The exceptions are alluvial fans that were formed by the right tributaries of the Sava River; gravel with sand is dominant in their lithological composition. The best hydrogeo- Keywords: lithological composition, alluvial fan, logical properties of the aquifer system were registered in the vicinity of the Sava River, so all Quaternary aquifer, hydrogeological characteristics, large pumping sites are located close to the river. The Quaternary aquifer is the main source of Sava River, Croatia the water supply in the Sava River valley. 1. INTRODUCTION geological framework: the mountain ranges and the narrow inter- mountain valley. Mt. Medvednica and Mt. Moslovačka gora as The geological framework is defined by the form and develop- well as the Slavonian Mountains (Mt. Papuk, Mt. Krndija, Mt. ment of the valley structure as well as the lithology and deposi- Psunj, Mt. Požeška and Mt. Dilj) are situated at the north end of tional environments within it. Structural deformation, volcanism the Sava River valley. At the southern end, the valley is bounded and erosion determine the geometry of the mountains as well as by Mt. Žumberak-Samoborsko gorje in Croatia as well as Mt. Pro- the extent and depth of the valley (HOLLETT et al., 1991). These sara, Mt. Motajica and Mt. Majevica in Bosnia and Herzegovina. structures and the lithology strongly control the permeability and These mountains were uplifted during the Pliocene epoch and storage characteristics of the deposits. Quaternary period (PAVELIĆ, 2001; ŠPARICA et al., 1972a,b; The Sava River valley is situated in the southwestern (SW) 1983; ŠPARICA & BUZALJKO, 1984; ŠPARICA, 1987). part of the Pannonian Basin (Fig. 1). In its wider area, two princi- The Sava River valley is filled with Neogene and Quaternary pal topographic features represent the surface expression of the sediments. Along the southern margin, the maximum depth to Figure 1. Location of the Pan­ nonian basin showing the po­ sition of the Sava basin and Sava River valley (simplified after Horváth, 1993). Legend: 1 – Mt. Medvednica, 2 – Mt. Mo­ slo va čka gora, 3 – Mt. Papuk, 4 – Mt. Krndija, 5 – Mt. Psunj, 6 – Mt. Po že ška, 7 – Mt. Dilj, 8 – Mt. Žum be račko­Samoborsko gorje, 9 – Mt. Prosara, 10 – Mt. Mo tajica and 11 – Mt. Majevica 202 Geologia Croatica 70/3 the pre-Miocene deposits reaches 4000 m (PRELOGOVIĆ, 1975; boreholes are unevenly distributed in the valley, but most of them HERNITZ, 1983). The older Quaternary boundary (Lower Pleis- are in the wider area of the Zagreb aquifer. Data from the bore- tocene-Middle Pleistocene) is defined by the conditional E-log holes were used to update the hydrogeological knowledge of the marker Q’ (URUMOVIĆ et al., 1976). According to URUMOVIĆ valley. A series of lithological cross-sections are presented in this et al. (1976), Q’ represents the most imposing lithostratigraphic study, and new groundwater level data were used to improve the boundary and can be tracked as a regional discontinuity during definition of the conceptual hydrogeological model. Geologia Croatica deposition. Above this marker, the coarse-grained sediments, gravel and sand, were deposited, while underlying sediments are 2. GEOLOGICAL STRUCTURES OF THE SOUTH- silt and clay. The Q’ marker lies at a maximum depth of 300 m WESTERN PART OF THE PANNONIAN BASIN (HERNITZ, 1983). The groundwater that accumulates in the The geodynamic evolution of the Pannonian Basin (PB) has been sandy and gravelly aquifers above marker Q’ is the main source discussed in many detailed and comprehensive studies (STEGENA of the water-supply for the whole region. et al., 1975; ROYDEN et al., 1983; KÁZMER & KOVÁCS, 1985; The aim of this paper is to determine the geometry of the ROYDEN & HORVÁTH, 1988; RATSCHBACHER, 1991; Quaternary aquifer system in the Sava River valley, as well as CSONTOS et al., 1992; HORVATH, 1993; DECKER & PERES- highlighting its lithological and hydrogeological characteristics. SON, 1996; PERESSON & DECKER, 1997). The southern PB, Data from approximately 500 boreholes and an additional 40 which extends from eastern Slovenia through northern Croatia wells have been collected for the purposes of this research. The and from northern Bosnia to Serbia, as well as its evolution, is de- Figure 2. Classification of structures and faults (Prelogović et al., 1998). Figure 3. Cross­section through the Sava basin (Prelogović et al., 1998). Brkić Željka: The relationship of the geological framework to the Quaternary aquifer system in the Sava River valley (Croatia) 203 Geologia Croatica scribed by TARI & PAMIĆ (1998), PRELOGOVIĆ et al. (1998), records were selected for construction of lithological profiles VELIĆ (1983). The PB includes the Drava River basin in the north throughout the Sava River valley. The boreholes that are located and the Sava River and Slavonija-Srijem basins in the south of along the Sava River were used for a longitudinal lithological northern Croatia. profile, while a series of boreholes perpendicular to the valley di- In this paper, the focus is on the Sava River basin. rection was grouped to display cross-sections of the valley. The The evolution of the southwestern Pannonian Basin occurred cross-sections show the lithology present in each borehole and during continued convergence between the Adriatic plate and the correlations between boreholes. Geophysical investigations were Southern Alps/Dinarides. According to PRELOGOVIĆ et al. also undertaken to define the boundaries, shape and depths of the (1998), the most important transcurrent faults that were active in aquifers. this stress field are the Periadriatic fault and its extension in the The boundaries of the aquifer layers with different hydraulic Drava fault and the fault along the margin of the Dinarides, which conductivity values were identified using pumping test data and here is referred to as the southern marginal fault of the PB (Fig. grain-size analysis of non-coherent deposits. 2). Between these faults, transpression occurred during the The lithological composition of the overlying layers is dis- Pliocene and Quaternary. Highlighted compressional structures played based on soil data for the first 4 m of the overlying layer were formed between the Sava and the Drava faults – the depth. Data were collected from the Faculty of Agriculture of the Žumberak–Medvednica Mountains structural unit, the Slavonian University of Zagreb (VIDAČEK et al., 2002). Mountains unit and the Moslavačka gora Mountains unit. Dis- placement and rotation of the uplifted mountain ranges reduced 4. RESULTS AND DISCUSSION the area of the surrounding basins. 4.1. Geometry and lithological characteristics The Sava fault zone is illustrated by the transverse cross- of the Quaternary aquifer section of the Sava basin (PRELOGOVIĆ et al., 1998). An asym- The boundary between the Pliocene and Pleistocene epochs has metric basin was formed during the Miocene epoch. Several not been defined with confidence (BAČANI et al., 1999). Most faults within the basin as well as the SW boundary faults were researchers have concluded that the transition from the Pliocene reactivated as reverse faults during compression in the Pliocene to the Pleistocene was gradual. It is believed that climatological, and Quaternary (Fig. 3). environmental and lithological continuity exists from the Plio- PAVELIĆ (2001) indicated that the evolution of northern cene to the Pleistocene (MAGAŠ, 1986). Because of the constant Croatia and northern Bosnia, as a part of the marginal zone of the lowering of the Sava Basin, the type of sedimentation remained Pannonian Basin, is interpreted as resulting from continental rift- the same, mostly from marshes, and the mineral composition ing. The Sava basin, together with the Drava basin, Požega val- changed only partially, suggesting a change in areal distribution ley, and the trough along the southern margin of Mt. Motajica in (An. ŠIMUNIĆ et al., 1973). northern Bosnia, form an elongated half-graben due to tectonic Palaeoclimate conditions in the Middle and Upper Pleis- subsidence along listric and strike-slip faults. tocene played the main role in the transport and deposition of The Pliocene epoch and most of the Quaternary period rep- clastic sediments. Alternatively, during the warm and humid pe- resented a